This invention generally relates to flame retardant thermoplastics and in particular high-temperature-processed polymers containing a flame retardant amount of phospham.
The addition of halogenated compounds to retard the flammability of thermoplastics is known. Such halogen compounds, however, pose various problems such as corrosion, discoloration and release of acid gases upon incineration. They also cause environmental concerns in connection with disposal of used plastics and scrap.
It is further known to retard the flammability of polymers by employing various phosphorus and phosphorus-nitrogen compounds. For instance, red phosphorus has been employed but because of perceived hazards of the dust igniting and possible generation of toxic phosphine or white phosphorus, it has not achieved wide acceptance. Polymers processed at lower temperatures can have flame retardation by use of ammonium polyphosphate or organic phosphates. Polymers processed at higher temperatures, such as above about 200.degree. C., however, are damaged by such additives, probably due to acid formation. It has been especially difficult to retard the flammability of nylon 4.6 which is processed above 300.degree. C., because only a few aromatic halogen additives (which entail the problems mentioned above) have enough stability. It has not hitherto been possible to find a phosphorus-based flame retardant additive with enough stability or inertness towards the polyamide.
Various formulations making use of ammonium polyphosphate or phosphorus oxynitride have been proposed for the flame retardation of polymers, as for example by Nason and Nielsen, as described in U.S. Pat. No. 2,661,341 (1953). However, these phosphorus-oxygen-nitrogen-containing materials are subject to acid development under the high temperature conditions of processing, necessary for many thermoplastics, and also under conditions where electrical resistance is often of importance.
An object of the present invention is to solve the above discussed problems of conventional flame retardants by providing a flame retardant formulation for polymers, especially for polymers processed at above about 200.degree. C., in particular styrene polymers, polyolefins and polyamides and more particularly, nylon 4.6 with no significant polymer degradation.